The uses of roller rocker and hydraulic tappet valve mechanism in the overhead cam engine structure are increasingly widespread, compared with the mechanical tappet valve mechanism, it has the following advantages: 1) compensate the valve clearance in a timely manner, requiring no periodical manual adjustment; 2) reduce the engine noise and shock; 3) small volume and weight, small friction and small kinematic inertia, which can reduce energy loss and improve engine efficiency; 4) Long life of the parts of valve mechanism, reducing the maintenance costs.
A columnar-type hydraulic tappet has a tank-shaped housing, provided with a tank-shaped housing, a plunger moving axially with respect to the housing being mounted in an inner cavity of the housing, a high pressure cavity used for a hydraulic medium extending between a lower end surface of the plunger and a lower side of the housing, the high pressure cavity being sealed by a unidirectional valve opened towards the high pressure cavity; a reset spring is arranged in the high pressure cavity, being between the lower end surface of the plunger and the housing. An oil hole used for hydraulic medium circulation is arranged at the housing, the oil hole is connected to an oil inlet hole of the plunger at a radial inner side of the housing, and an oil chamber used for storage of hydraulic medium is formed between the plunger oil inlet hole and the unidirectional valve.
The Chinese patent document CN102767405 discloses a hydraulic support member, which is a split structure composed of an upper plunger body and a lower plunger body. It has the advantages of low difficulty of processing for individual parts and proneness to remove the wastes producing from the cavity of the plunger; but its two parts are required to processing separately, which adds the machining processes, with low machinery efficiency and high production costs; especially it has high requirement of runout of the contact end surfaces of two plunger bodies. If the runout is poor, it may produce a lateral force and cause stuck of plunger body in the housing, which may restrict the uses of the product. In addition, if a punching process is adopted for a plunger oil inlet hole, sometimes the wastes cannot be completely punched to adhere to the inner wall, and there will be burrs if separated, affecting the product performance when falling in use; and if drilling and milling process are adopted, burrs may be left in the hole of inner wall, having risks.
The Chinese patent document CN201228569 discloses a hydraulic support member whose plunger is an integrated-type structure, with a steering member inside. Its drawback is that the processing of plunger cannot be completed at one time, requiring multiple processes, time and labor consuming. With such a structure of plunger oil inlet hole, wastes will inevitably generated when processing oil inlet holes. The plunger cavity of this kind of structure does not have a large outgoing channel, so the wastes produced cannot be removed completely. In addition, the wastes generating from hole processing may not be completely cut off but attached to the inner wall of the plunger, increasing the difficulty of waste removal.